What happens if I miss the 90-day report in Thailand and then return after leaving the country?

Oops, sorry. I read your first post as 20,000, rather than 2,000. My mistake. 2,000 is a completely reasonable fine for what the person did (not file for a whole year). That makes perfect sense. If it happened repeatedly (year after year) and I were his Immigration Officer I would start fining him 5,000 baht because, in my opinion, he is being flagrant about breaking the rule.

On the other hand, good to know that if you disregard this rule you will likely only face 2,000 baht per year. ;-) However, he may also be getting a stamp in his passport indicating he routinely doesn't file a 90-Day Report. There are no official consequences for doing that but I'm pretty sure I wouldn't want that in my passport.

Man, the person you know must have really pissed his immigration officer off! The only way it makes sense to me (legally speaking) is that he didn't do 90-Day Reports for a whole year (or longer) and they decided to charge him the maximum fine of 5,000 (for flagrant violations) for each 90-Day period he missed. That's really unusual! But you know what, sometimes you can really piss off an immigration officer and then they rack their brains for ways they can stick it to you, so I don't discount your story. But like I said very unusual. You have to work pretty hard to piss off immigration officers that badly ;-)

Annika Almersson I have not heard that, but I guess anything is possible. Just checking with you that we're talking about the 90-Day Report that one on a long-term stay needs to file when he has been in Thailand for 90 days, and not some sort of visa where he needs to leave every 90 days. The worst fine possible in the law is 5,000 baht for flagrant violations of the 90-Day Report rule. I've never heard of anyone even getting that high a fine for this reason. The 20,000 sounds like the sort of fine you get for an overstay. Not doing a 90-Day Report will never get you on overstay, those are two different things.